1. Field of the Invention
The present invention relates to lubricating oil compositions which contain oil soluble hydroperoxidized polymeric additives which improve the sludge and varnish dispersancy as well as improving the viscosity index characteristics of the lubricating oil.
2. Description of the Prior Art
An important property of a lubricant composition is the rate at which its viscosity changes as a function of temperature. The relationship between the viscosity and temperature is commonly expressed in terms of the viscosity index (V.I.). Lubricant compositions which change little in viscosity with variations in temperature have greater viscosity index than do compositions whose viscosity is materially affected by changes in temperature. It is readily apparent, therefore, that one of the major requirements of lubricating oils or other hydrocarbon oil products is their satisfactory viscosity-temperature characteristics. These characteristics are necessary in order that the oil's viscosity will not become too low but will show an equally good performance within a relatively wide temperature range to which it may be exposed in service. The wider the possible temperature variations, the smaller should be the change in viscosity with temperature. Hence, the viscosity-temperature characteristics of a lubricant which is used in applications where wide variations in temperature are encountered are of great importance and lubricant compositions having high viscosity indices are highly desirable.
Also, lubricants for modern, high compression, piston-type internal combustion engines must necessarily have high detergency properties, i.e., they must have efficient sludge and varnish dispersant action and chemical and thermal stability in order to free the engines from deposits of varnish, sludge and coke-like materials. Generally, a heavy duty detergent type slubricating oil is employed in such engines in order to maintain the desired high degree of engine cleanliness and thereby promote longer engine life.
A variety of polymeric or high molecular weight materials have been described as viscosity index improvers for lubricants. For example: U.S. Pat. Nos. 3,551,336 and 3,691,078 teach the preparation of ethylene copolymers which act as viscosity index improvers for lubricants.
U.S. Pat. No. 3,417,020 teaches a process for preparing viscosity index improvers by reacting an olefinic polymer with ozone and reduction of the resulting ozonolysis product until carbonyl groups are formed thereon.
U.S. Pat. No. 3,417,020 teaches lubricating oil compositions of improved viscosities containing degraded ethylene-alpha-olefin polymers wherein the degraded polymers have been hydroxylated. The hydroxylated degraded polymers are prepared by hydroperoxidizing the polymer with subsequent reduction of the hydroperoxide groups to yield degraded products containing hydroxyl groups and minor amounts of carboxyl, keto and aldehyde groups
U.S. Pat. No. 3,756,954 teaches the preparation of viscosity index improvers prepared by air oxidation of interpolymers of ethylene and propylene in the presence of an aliphatic amine.
British Patent No. 2,040,296A teaches the preparation of a viscosity index improver additive by oxidatively and mechanically degrading an ethylene copolymer containing as one of its components from 0.05 to 3% of 2,5-norbornadiene.
Also, a variety of compositions comprising polymeric or high molecular weight materials which incorporate nitrogen have been described as dispersants and as viscosity index improvers for lubricants. For example:
U.S. Pat. No. 3,316,177 teaches reaction of polyamine with the reaction product of maleic anhydride with an oxidized interpolymer of ethylene and propylene, as a sludge dispersant in lubricant and fuel compositions.
U.S. Pat. No. 3,404,091 describes the preparation of nitrogen containing polymers, useful as sludge dispersants and viscosity index improvers, by grafting polar monomers such as acrylonitrile onto hydroperoxidized ethylene-propylene copolymers.
U.S. Pat. No. 3,404,092 describes the preparation of polymeric viscosity index improvers containing urethane groups by the reaction of hydroxylated ethylenepropylene copolymers with isocyanates.
U.S. Pat. No. 3,687,849 describes the preparation of viscosity index improvers, pour point depressants and dispersants, for fuels and lubricants, by grafting various unsaturated monomers onto a degraded, oxidized, interpolymer of ethylene and propylene.
U.S. Pat. No. 3,687,905 describes the preparation of additives for fuels and lubricants by the reaction of an unsaturated acid, such as maleic acid or anhydride, with an oxidized, degraded interpolymer of ethylene and propylene, followed by reaction with a polyamine.
British Patent No. 983,040 describes the preparation of detergent additives for lubricants by the reaction of a polyamine with a long chain monocarboxylic acid prepared by oxidation of an olefin polymer.
British Patent No. 1,027,410 describes the preparation of ashless detergents for lubricating oils by the reaction of a polyhydroxyamine with a polymeric monocarboxylic acid.
British Patent No. 1,172,818 describes the preparation of additives for lube oils by the condensation of an amine with an ozonized polymer.
U.S. Pat. No. 3,769,216 discloses the preparation of lube oil additives by the condensation of an amine with an oxidized ethylene-propylene copolymer, prepared by air blowing in the presence of a peroxide (also see U.S. Pat. 3,785,980), or by mastication of the polymer in the presence of oxygen.
We have now found, however, that dispersant-viscosity index improvers for lubricating oils may be prepared from hydroperoxidized ethylene copolymers and terpolymers which additives contain an excess of carboxylic acid groups over hydroxyl groups, and, further, that functionalization with amines is not required.